Such methods and apparatuses are usually used in order to produce three-dimensional objects in layers. A three-dimensional object is produced here by selectively solidifying successive layers of a powdery material at the appropriate locations of a respective cross-section of the object, for example by selectively applying a binder to the respective layer and setting the binder, by introducing a binder into the respective layer and selectively setting the binder, or by subjecting the respective layer selectively to the action of a laser beam.
WO 00/78485 A2 discloses a coating device for applying flowable material across the surface of a substrate in individual layers one above the other. As can be seen from FIG. 4, the coating device 3 has a metering shaft which can be displaced back and forth over the substrate, having two spaced-apart walls 4, 5 which extend over the entire width of the substrate to which the layers are applied and, between them, form a shaft 6 which is open toward the top and the bottom. At their bottom end, adjacent to the surface 1, the walls 4, 5 have smoothing elements 7, 8, which may be designed, for example, as rubber lips or as metal blades. As an alternative, the smoothing elements are formed from ceramic material. At its two opposite ends, or at one end, the coating device 3 is guided in the frame of the device and driven so as to allow back and forth movement of the metering shaft over the entire surface 1, and thus application of the respective layer, in a predetermined layer thickness, to the substrate. A stationary supply container 9 is provided which is borne by the machine frame 10, and likewise forms a shaft 13 which is open toward the top and the bottom.
During operation, powder is introduced, in an end position of the coating device 3, into the shaft 6 of the latter from the stationary supply container. When the coating device 3 is then moved away, self-levelling of the flowable powder in the supply container takes place by way of the pile which builds up. If the supply container is very wide, and also relatively narrow in terms of depth, it may be the case that the powder has to be distributed in the supply container by means of vibrators or of a distributing worm. This is the case, in particular, when use is made of powder with poor flow properties, in which case the pile is very steep.
Mechanical distribution by means of a distributing worm or of vibrators means that the powder in the supply container is subject to very different levels of compaction along the supply container. This results in locally different metering quantities in the displaceable supply container of the coating device, metering taking place in the end position of the same, and this may ultimately result in locally different levels of compaction in the building zone and thus in quality fluctuations in respect of strength, finish and component compaction. In order to avoid inhomogeneity, when the supply container is refilled, on account of residues which have a density which differs from that of the newly introduced powder, the supply container is usually completely emptied and/or zeroed. However, this produces further quantities of waste.